Spinal cord injury in experimental thoracic aortic occlusion: investigation of combined methods of protection

Abstract

The efficacy of combined methods of spinal cord protection during thoracoabdominal aortic reconstruction was evaluated because a recent clinical study failed to substantiate the value of cerebrospinal fluid drainage when used alone in the prevention of paraplegia. The effect of cerebrospinal fluid drainage and aortofemoral shunting were analyzed with regard to neurologic outcome and spinal cord blood flow in a model of thoracic aortic occlusion. In addition, we studied the use of motor-evoked potentials as compared with somatosensory-evoked potentials in monitoring cord perfusion. Thirty-two dogs underwent proximal and distal thoracic aortic occlusion for 60 minutes. The control group (n = 8) underwent thoracic aortic cross-clamping only. Spinal cord protection was used in three groups: cerebrospinal fluid drainage alone (n = 8), aortofemoral shunting alone (n = 8), and cerebrospinal fluid drainage and aortofemoral shunting (n = 8). Neurologic outcome improved in all treatment groups as compared with controls (p less than 0.001). The addition of cerebrospinal fluid drainage to aortofemoral shunting did not further improve neurologic outcome. Spinal cord blood flow measured with microspheres in the lumbar gray matter was significantly higher in the dogs with aortofemoral shunting (+/- cerebrospinal fluid drainage) as compared with those with cerebrospinal fluid drainage alone (p less than 0.05) or the controls (p less than 0.001). Aortofemoral shunting also prevented the development of acidosis and hyperglycemia. Loss or changes in amplitude and latency of motor-evoked potentials did not distinguish between the groups. Loss of somatosensory-evoked potentials had a high sensitivity (92%) but lower specificity (68%) in predicting neurologic injury, whereas loss of motor-evoked potentials had a high specificity (100%) but a very low sensitivity (16%). We conclude that cerebrospinal fluid drainage or aortofemoral shunting significantly improve spinal cord blood flow and neurologic outcome. The greatest increase in spinal cord blood flow was seen with aortofemoral shunting, which also prevented metabolic disturbances of reperfusion. Although the addition of cerebrospinal fluid drainage to aortofemoral shunting was the only group in which no neurologic injury occurred, this group did not have a significant improvement in outcome when compared with aortofemoral shunting alone. Spinal cord ischemia was more accurately detected with somatosensory-evoked potentials when aortofemoral shunting was used, whereas motor-evoked potentials recorded from the spinal cord were not sensitive enough to predict neurologic injury.

Strategies for Spinal Cord Protection during Descending Thoracic and Thoracoabdominal Aortic Surgery: Up-to-date Experimental and Clinical Results - A review

“…In any case, cerebrospinal uid drainage cannot be regarded as the only and most effective maneuver to improve spinal cord blood ow. Elmore et al (79) showed that after 60 min of thoracic aortic occlusion in a dog model, spinal cord blood ow was signi cantly increased by cerebrospinal uid drainage as compared with controls as shown also by Bower et al (76). However, spinal cord blood ow was more than doubled by using aortofemoral shunt as compared with cerebrospinal uid drainage alone.…”

“…In fact, passive shunts seem to provide suboptimal blood ow and perfusion pressure (<40 mmHg), whereas atriofemoral or femoro-femoral bypasses can adjust the mean distal aortic pressures between 60 and 70 mmHg (98), values which are more likely to maintain a spinal cord perfusion pressure above 40 mmHg (43). Furthermore, a better control of the proximal aortic and pulmonary artery pressures can be achieved without pharmacologic intervention (79), with potential positive effect on intracranial and cerebrospinal uid pressure.…”

“…Controversial experimental (76,79,80) and clinical results (77,(80)(81)(82)(83) have been reported with monitoring of cerebrospinal uid pressure and its drainage, and these are probably due to the fact that several other factors also in uence spinal cord perfusion pressure, and not necessarily result in an increase of cerebrospinal uid pressure. In fact, intraoperative and postoperative hypotension and the use of vasodilators to control proximal aortic hypertension can severely impair the spinal cord perfusion by reducing the spinal artery pressure (84)(85)(86), and this parameter is signi cantly in uenced also by the presence and position of the distal aortic clamp, the use or not of distal aortic perfusion and the degree of perfusion pressure.…”

“…Elmore et al (79) reported the results of a canine model of spinal cord ischemia in which they were able to demonstrate a distinct increase in spinal cord blood ow by using distal aortic perfusion during 60 min of aortic cross-clamping. Such an increase in blood ow was signi cantly higher than in controls and in animals in which only cerebrospinal uid drainage was performed.…”

Spinal Cord Protection During Thoracoabdominal Aneurysm Repair

“…The centrifugal pump is used for left heart bypass, 3,28,39 and provides the best means of maintaining distal aortic perfusion. By using centrifugal pumps flow can be regulated, there is less damage to the blood components than with roller pumps, minimal heparinization is required, and a reservoir can be used in the setting of trauma or a ruptured aneurysm.…”